Flexible and surface-mountable piezoelectric sensor arrays for underwater sensing in marine vehicles

In an effort to improve the situational awareness and obstacle avoidance of marine vehicles, we fabricate, package and characterize (Zr _0.52Ti_0.48)O₃ thin-film piezoelectric pressure sensor arrays for passive fish-like underwater sensing. We use floating bottom electrode in designing the sensor which made the sensor able to detect very low frequency range (down to 0.1 Hz) in water. The proposed array of sensors is capable of locating underwater objects by transducing the pressure variations generated by the stimulus. The sensors are packaged into an array of 2 × 5 on a flexible liquid crystal polymer substrate patterned with gold interconnects. Experiments in this paper are divided into three main categories. First, in order to evaluate the effect of water on the sensor performance, resonant frequency, and quality factor changes in air and water are investigated theoretically and experimentally. Second, the ability of the array in locating a vibrating sphere (dipole) in water is illustrated through experiments. The sensors demonstrate a high resolution of 3 mms^-1 in detecting in detecting oscillatory flow velocity in water. Third, 'real-time' experiments are conducted in a swimming pool environment by surface mounting two arrays of sensors on the curved hull of a kayak vehicle. The arrays are self-powered and do not need any external power supply, to operate, which greatly benefits in eliminating the need of bulky power supplies on underwater vehicles.